Estimating an average effect in meta-analysis is the process of combining the effect sizes from the set of studies collected for the meta-analysis. Meta-analysis is a study of studies where research synthesis is performed through statistical aggregation of empirical research reports. Meta-analysis allows scholars to clarify inconsistent or discrepant findings in a research literature. Among others, meta-analysis serves two useful functions by allowing for the possibility of (a) estimating a weighted mean effect size from a sample of cases (the subject of the present entry and what many people would call the main function of a meta-analysis) and (b) testing moderating variables that may account for discrepant findings in research literature (which is beyond the scope of this entry). There are many steps to a ...